Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity.
In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Once the catheter is positioned within the heart, the location of aberrant electrical activity within the heart is then located.
One location technique involves an electrophysiological mapping procedure whereby the electrical signals emanating from the conductive endocardial tissues are systematically monitored and a map is created of those signals. By analyzing that map, the physician can identify the interfering electrical pathway. A conventional method for mapping the electrical signals from conductive heart tissue is to percutaneously introduce an electrophysiology catheter (electrode catheter) having mapping electrodes mounted on its distal extremity. The catheter is maneuvered to place these electrodes in contact with the endocardium. By monitoring the electrical signals at the endocardium, aberrant conductive tissue sites responsible for the arrhythmia can be pinpointed.
For sensing by ring electrodes mounted on a catheter, lead wires transmitting signals from the ring electrodes are electrically connected to a suitable connector in the distal end of the catheter control handle, which is electrically connected to an ECG monitoring system and/or a suitable 3-D electrophysiologic (EP) mapping system, for example, CARTO, CARTO XP or CARTO 3, available from Biosense Webster, Inc. of Irwindale, Calif.
The closely-spaced electrode pairs allow for more accurate detection of near-field potentials versus far-field signals, which can be very important when trying to treat specific areas of the heart. For example, near-field pulmonary vein potentials are very small signals whereas the atria, located very close to the pulmonary vein, provides much larger signals. Accordingly, even when the catheter is placed in the region of a pulmonary vein, it can be difficult for the electrophysiologist to determine whether the signal is a small, close potential (from the pulmonary vein) or a larger, farther potential (from the atria). Closely-spaced bipoles permit the physician to more accurately remove far field signals and obtain a more accurate reading of electrical activity in the local tissue. Accordingly, by having closely-spaced electrodes, one is able to target exactly the locations of myocardial tissue that have pulmonary vein potentials and therefore allows the clinician to deliver therapy to the specific tissue. Moreover, the closely-spaced electrodes allow the physician to determine the exact anatomical location of the ostium/ostia by the electrical signal.
However, manufacturing and assembling catheters with closely and precisely spaced ring electrodes pose many challenges. Accuracy and consistency in spacing between adjacent electrodes become critical to catheter manufacturing and assembly. Conventional methods often use adhesives such as polyurethane to seal each ring electrode, which creates a margin between adjacent electrode or electrode pairs that can limit how closely the electrodes can be spaced from each other. Typically, spacing of 1.0 mm or larger between electrode pairs can be achieved using such conventional methods. However, spacing smaller, especially 0.2 or 0.1 mm spacing is difficult to achieve. With such smaller spacing, there is the risk of adjacent electrodes coming in contact due to electrode tolerance specification or shifting of electrodes during assembly when medical grade adhesive such as Polyurethane is applied or when medical epoxy is curing.
Moreover, the conventional methods of attaching a lead wire to a ring electrode also typically require spacing tolerances between adjacent ring electrodes. Such attachment methods often result in an acute angle at which the lead wire must extend to reach the ring electrode which can cause stress leading to detachment or breakage.
Flexible electronics, also known as flex circuits, is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film. Additionally, flex circuits can be screen printed silver circuits on polyester. Flexible printed circuits (FPC) are made with a photolithographic technology. An alternative way of making flexible foil circuits or flexible flat cables (FFCs) is laminating very thin (0.07 mm) copper strips in between two layers of PET. These PET layers, typically 0.05 mm thick, are coated with an adhesive which is thermosetting, and will be activated during the lamination process. Single-sided flexible circuits have a single conductor layer made of either a metal or conductive (metal filled) polymer on a flexible dielectric film. Component termination features are accessible only from one side. Holes may be formed in the base film to allow component leads to pass through for interconnection, normally by soldering.
Accordingly, a need exists for an electrophysiological catheter with bipole microelectrode pairs that are very closely spaced to minimize detection of noise and/or far-field signals. There is also a need for a method of manufacture and assembly of such a catheter wherein very close spacing between electrodes can be achieved readily and consistently with improved precision and accuracy.